a. Field of the Invention
The present invention pertains to data transmission systems and specifically to packetized data transmission busses.
b. Description of the Background
Packetized data transmission busses are commonplace in today's electronic systems. Each transmission has a maximum size and typically has a start of frame character, a preamble, the data payload, a checksum, and an end of frame character. The specifications of the transmissions are defined in the various standards and specifications of the particular data bus. TCP/IP and SATA/SAS are examples of packetized data transfer protocols.
The transfer of a large block of data is normally broken into several small transmissions according to the specification of the protocol. If the maximum data payload is 8 K bytes, then each transmission contains 8 K bytes of information. As many individual packets are transmitted as necessary to complete the large block of data.
Packetized data transfer protocols do not necessarily stress the data transfer hardware because data is sent in small bursts. The data transfer bus or network may be able to handle continuous high-speed traffic, however the device connected to the bus or network may only need to transmit at high speed for the time required to send or receive an individual packet.
An interface to a packetized data transfer protocol may have many functions performed in hardware. For example, the process of taking a large data block, breaking the data into packets, adding the appropriate characters to the beginning and end of the packets, and transferring the packet onto the data bus may be implemented by preconfigured logic in an integrated circuit. A routine implemented as an integrated circuit has the ability to operated very fast while being a very low cost.
When a packetized data bus is implemented in a hardware interface, the interface may be physically restricted to only transmitting data in discrete packets. In the development and testing of interface performance, including testing downstream devices and network throughput, the transmissions of discrete packets of data may not reveal design or performance problems with the transmission scheme. Certain design flaws or manufacturing defects may only be apparent when continuous transmissions are passed across the data bus. Such flaws or defects may be only marginally detectable during normal operation with discrete packets, but may be very obvious during continuous transmissions.
It would therefore be advantageous to provide a system and method for operating a packetized data bus interface in a mode wherein the data packets may exceed the standard data packet size. It would be further advantageous to make the mode selectable for testing, debugging, and characterizing of the data bus.